The present invention relates to an electro-photographic apparatus and a process-cartridge.
In recent years, electrophotographic photosensitive members comprising various organic photoconductor compounds as principal components have been extensively developed. For example, U.S. Pat. No. 3,837,851 has disclosed an electrophotographic photosensitive member having a charge transport layer comprising a triarylpyrazoline.
U.S. Pat. No. 3,871,880 has disclosed an electrophotographic photosensitive member having a charge generation layer comprising a perylene pigment derivative and a charge transport layer comprising a 3-propylene-formaldehyde condensate.
Organic photoconductor compounds have their own different sensitive wavelength regions. For example, Japanese Laid-Open Patent Application (JP-A) 61-272754 and JP-A 56-167759 disclose compounds showing a high sensitivity to a visible region.
JP-A 57-195767 and JP-A 61-228453 disclose compounds showing a high sensitivity to an infrared region.
Among these compounds, those having a sensitivity to an infrared region are used in laser beam printers, digital copying machines and LED printers, and the demand therefor is becoming intense.
As representative charge-generating substances showing a sensitivity to the infrared region, phthalocyanines are known, and among these, oxytitanium phthalocyanine showing a high sensitivity has been extensively studied.
For example, oxytitanium phthalocyanine is 10 known to have many crystal forms similar to other phthalocyanine compounds, and many studies thereon have been made.
Specific examples of such crystal forms may include those disclosed in JP-A 61-239248, JP-A 62-67094, JP-A 1-17066, JP-A 3-54264, and J7P-A 3-128973.
Oxytitanium phthalocyanine has a high sensitivity, but is accompanied with a problem that its potential characteristic is liable to vary on repetitive use.
On the other hand, as exposure means for forming electrostatic latent images on an electrophotographic photosensitive member, it has been known to use a rotating multi-face mirror (so-called a polygonal mirror as used hereinbelow) for reflecting a laser beam from a semiconductor laser to illuminate the photosensitive member surface.
In the case of such exposure means using a laser beam, it is necessary to accelerate the laser beam scanning speed in order to realize high-resolution output images or high-speed output images by using a single laser beam. However, a certain upper limit is present regarding the rotation speed of a polygonal mirror.
Accordingly, for solving the problem, there has been proposed and realized a multi-beam (scanning) scheme wherein an electrophotographic photosensitive member is scanned with a plurality of laser beams simultaneously.
The multi-beam scheme has the advantages described below.
In the case of using an identical laser beam scanning speed for realizing an identical printing speed in an image forming apparatus using a number (n) of laser beams, the scanning line density can be raised to n-times that in an apparatus using a single laser beam, thus making it possible to realize a higher-resolution image recording.
On the other hand, in the case of realizing identical scanning speed and scanning density of laser beam as in the case of a single laser beam scheme, the printing speed can be raised as high as n times. Further, in the case of using identical printing speed and scanning density, it becomes possible to lower the laser beam scanning speed and accordingly the rotation speed of a polygonal mirror to 1/n times those in the single-beam scheme, thus allowing simplification of the polygonal mirror drive mechanism and a lower production cost.
However, in an already realized electrophotographic apparatus using exposure means of the multi-beam scheme, there has been encountered a difficulty that output image densities can be different regardless of identical electrostatic latent image formation depending on whether a plurality of adjacent laser beams are emitted simultaneously or the laser beams are emitted individually and sequentially.
Moreover, in an electrophotographic apparatus not equipped with a charge-removal means, such as pre-exposure means, a ghost phenomenon is liable to be more pronounced that an image of a subsequent cycle is affected by a history of an exposed part in a preceding cycle than in the case of using a single laser beam.
These phenomena are liable to occur more noticeably in the case of using oxytitanium phthalocyanine as a charge-generating substance for an electrophotographic photosensitive member.
An object of the present invention is to provide an electrophotographic apparatus which is less liable to cause a density difference regardless of laser beam emission state, or ghost or potential fluctuation on repetitive use even in a system of using a multi-beam exposure means and without a charge-removal means, such as pre-exposure means.
Another object of the present invention is to provide a process-cartridge for such an electro-photographic apparatus.
According to the present invention, there is provided an electrophotographic apparatus, including: an electrophotographic photosensitive member comprising a support and a photosensitive layer thereon, a charging means for charging the photosensitive member, a multi-beam exposure means for illuminating the photosensitive member with a plurality of laser beams to form an electrostatic latent image on the photosensitive member, a developing means for developing the electrostatic latent image to form a toner image on the photosensitive member, and a transfer means for transferring the toner image from the photosensitive member to a transfer-receiving material, wherein
the electrophotographic apparatus is not equipped with a charge-removal means for uniformly charge-removing the photosensitive member in advance of operation of the charging means, and
the photosensitive member has a photosensitive layer containing oxytitanium phthalocyanine and exhibits a charge mobility of 7.0xc3x9710xe2x88x925 to 2.0xc3x9710xe2x88x925 cm2/volt.sec.
The present invention further provides a process-cartridge which includes the photosensitive member and at least one of the charging means and the developing integrally supported to form a unit, and is detachably mountable to a main assembly of the above-mentioned electrophotographic apparatus.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.